In a study just published in Frontiers in Marine Science, scientist have discovered that feces from corallivorous fish species may provide a source of beneficial microbes that help coral thrive. Until recently, these species were thought to weaken reef structures, while grazing species that consume algae and detritus were thought to keep reefs healthy. In a surprising twist, the scientists actually discovered that feces from grazers leaves large lesions on corals, possibly because they contain coral pathogens.
“Corallivorous fish are generally regarded as harmful because they bite the corals,” said Dr. Carsten Grupstra of Rice University, lead author of the study “But it turns out that this doesn’t tell the whole story. Corallivore feces contain many of the bacterial taxa that associate with healthy corals under normal conditions, potentially resulting in the natural dispersal of ‘coral probiotics,’ analogous to fecal microbiota transplantation therapy in humans.”
Grupstra and colleagues studied the effects of feces from both corallivores and grazers on live coral. They placed pieces of coral in jars with sterile seawater and applied feces from corallivore and grazer fish to different jars. Some samples were sterilised, to determine whether the physical characteristics of the feces alone caused the lesions. After the experiment, each piece of coral was examined and categorised as apparently healthy, containing lesions, or dead. Adding feces to the jars sometimes caused lesions on coral pieces, and potentially even the death of the fragment; fragments without any feces remained healthy. Feces from grazers caused lesions or death in all coral pieces, while feces from corallivores caused fewer and smaller lesions and rarely caused death. Sterilised feces from either type of fish caused little harm, comparable to the low levels of damage caused by corallivore feces.
The scientists suspected that this was because of the greater abundance of coral pathogens found in the fresh feces of grazers, and the higher abundance of beneficial microbes found in the fresh feces of corallivores. The fish previously assumed to be harmful may thus be contributing to important processes that promote coral reef health.
“More research needs to be done to test how fish feces affect corals to see how we might use these feces in management efforts to support coral reef health,” said Grupstra.
More information: Consumer feces impact coral health in guild-specific ways, Frontiers in Marine Science (2023). DOI: 10.3389/fmars.2023.1110346. www.frontiersin.org/articles/1 … rs.2023.1110346/full
Journal information: Frontiers in Marine Science